1. Field of the Invention
The present invention relates generally to the construction of vascular catheters. In particular, the present invention relates to catheters that require an inflation lumen connecting a proximal source of inflation medium with an inflatable element, such as a balloon, at the distal end of the catheter.
Atherosclerosis is a condition characterized by fatty-like deposits (atheromas) in the intimal lining of a patient's arteries. Atherosclerosis can have many symptomatic manifestations, including angina, hypertension, myocardial infarction, strokes, and the like. Initially, the atheromas deposited in the blood vessels are relatively soft and tractable; however, over time they become calcified and hardened.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, where a balloon-tipped catheter is used to dilatate a region of atheroma; atherectomy, where a blade or other cutting element is used to sever and remove the atheroma; and laser angioplasty, where laser energy is used to ablate at least a portion of the atheroma. In addition to such therapeutic approaches, a variety of techniques for transluminal imaging of atheroma and other diseased regions of a blood vessel has been proposed, including endoscopic imaging and ultrasonic imaging techniques.
Many of such techniques require the use of an inflatable element, such as a balloon, located near the distal end of the catheter. Balloon angioplasty, of course, utilizes a distal balloon as the primary interventional element. In addition, atherectomy, laser angioplasty and transluminal imaging may all utilize a balloon to position the distal end of the catheter within a blood vessel.
Of particular interest are atherectomy procedures which utilize special catheters having a severing instrument located at a distal end thereof and an inflatable balloon located opposite the severing instrument. The catheter is positioned within the vascular system so that the severing instrument lies adjacent the atheroma, and the balloon is inflated to bring the severing instrument into close proximity with the atheroma. The severing instrument is then actuated to excise the atheroma, and the severed material captured to prevent the release of emboli. The severing instrument on the atherectomy catheter can take a variety of forms, including fixed blades (requiring movement of the entire catheter to effect cutting) and movable blades which can be actuated without movement of the catheter as a whole. The present invention, however, is not limited to atherectomy catheters and instead is broadly adaptable to catheters that employ inflation techniques with a wide variety of interventional and imaging implements mounted in a distal housing.
Intravascular catheters are usually designed to be symmetric about their longitudinal axis. Preferably, the catheters have a circular cross-section in order to facilitate translation and rotation of the catheter within the patient's vascular system. Whenever an inflation balloon is placed at the distal end of the catheter, it is desirable that an inflation lumen be integrated into the catheter body without destroying the catheter's symmetric shape. This may be done in a variety of ways. For example, lumens may be formed in the wall of the catheter body while maintaining a desired symmetry. Alternatively, separate inflation tubes may be disposed within larger lumens within the catheter and connected with the distal balloon. A third approach is to form a coaxial sheath about the catheter body, where the sheath provides an annular lumen which may be connected to the balloon. Although each of these approaches maintains the desired symmetry, they each require that the overall cross-sectional area of the catheter be increased. Such an increase in area is undesirable, particularly when the catheter is to be used in coronary procedures or when it must pass through tight lesions.
Thus, in some cases, it would be desirable to reduce the total cross-sectional area of intravascular catheters to facilitate passage of the catheter through tight, tortuous regions of the vascular system even if such reduction requires a non-symmetric design. One way this may be accomplished is to provide an inflation lumen or tube external to the catheter body. Such a design eliminates unnecessary material in the catheter body which would be necessary in order to provide symmetry.
Whenever an external inflation lumen is provided on an otherwise symmetric catheter body, the resulting ridge gives the catheter a non-symmetric shape. The non-symmetric shape may be acceptable for those applications in which rotational movement of the catheter is not required (e.g. balloon angioplasty with symmetric balloons) or is not constrained by the vessel walls; however, under tight-fitting conditions, use of such a non-symmetric catheter can be problematic. In particular, the non-symmetric shape can give rise to a phenomenon known as "catheter whip." Catheter whip occurs whenever the operator of the catheter attempts to rotate the catheter within the vascular lumen to rotationally align with a predetermined site of occlusion. When the operator must rotate the catheter, and the vessel passage is too narrow, the ridge presented by the external lumen of conventional designs can resist the motion. This resistance causes the buildup of potential energy (i.e., through a rotational wind-up) that can be released suddenly upon application of additional rotational force. This sudden release of energy resulting in uncontrolled rotational motion is known as "catheter whip." Catheter whip can similarly be induced upon application of torque to catheters having fixed cutting members at their distal ends to remove deposits from the vessel wall by rotation of the entire catheter. See, e.g., U.S. Pat. Nos. 4,627,436 and 4,685,458.
For the above reasons, it is desirable to provide intravascular catheters that have a symmetric or nearly symmetric shape without incorporating excess structural material which restricts the catheter's ability to enter narrow passageways. Such a design is expected to greatly reduce the occurrence of catheter whip.
2. Description of the Background Art
Atherectomy catheters having symmetric cross-sections with internal inflation lumens are described in European patent application 163 502 and U.S. Pat. No. 4,669,469. An embolectomy catheter having an external helical balloon at its distal end is described in U.S. Pat. No. 4,762,130. An atherectomy catheter having a non-symmetric construction is described in U.S. Pat. No. 5,071,425, the disclosure of which is incorporated herein by reference.